Brushless DC motors are often used to drive handheld work apparatus such as chain saws, cut-off machines, blowers, brushcutters, hedge trimmers, or the like.
Electronically commutated electric motors require defined starting conditions for starting the run-up so that the electronically commutated rotating field drives the rotor in the intended direction. Defined operating conditions are also required during the run-up of the motor to the operating speed. It must be ensured that the rotor can reliably follow the rotating field whose speed increases. It is known to operate the motor by means of running up according to predefined switching patterns during the run-up. If the rotor is slowed down unexpectedly during the run-up, this may cause the rotor to no longer be able to follow the rotating field of the stator and the motor fails to start. The starting of the brushless DC motor has failed.
To ensure a reliable run-up of an electronically commutated electric motor, it is known to provide positional sensors which detect the position of the rotor and pass the information on to the electronic control unit of the motor. For example, hall sensors are used which ensure that the rotating field is always switched to be adapted to the position of the rotor. Even when load suddenly occurs on the rotor, a run-up of the motor is ensured, since the rotating field is always adapted to the current position of the rotor.
When the operating speed is reached, the rotating field is controlled by the voltages induced in the field windings of the stator, whose magnitude and direction ensure a reliable control of the electronically commutated electric motor in the range of the operating speed.